It is known to use rotary presses for making tablets and similar compacts. These presses exhibit a rotor which is beared and driven rotatably about a vertical axis, wherein the rotor exhibits a die plate and punch guides for upper and lower punches. These upper and lower punches are controlled by appropriate cams, and in at least one press station an upper and a lower pressure roller are disposed, with the help of which the punches compress the material to be compressed which is present in the dies.
After the pressing process, some materials to be compressed tend to adhere to the pressing surface of the upper punches, when the upper punch starts its return stroke. This effect causes the surface of the compact not to have the desired quality and moreover has an adverse effect on the subsequent pressing process. From EP 0 448 190 B1 and DE 88 16 064 U1, it has become known to bear the punches rotatably in the punch guides and to set them in a rotationary motion during the return stroke after a pressing process. By means of the rotation of the punches, the adherence effect can be eliminated to a large extent. From DE 100 24 340 C2 it is also known to bear a punch insert rotatably in the punch shaft, wherein the insert exhibits a projection which is guided in a helical curve-fashion between two axially spaced guides. A spring biases the insert downwards away from the punch shaft.
During the return stroke of the upper punches, an unloading occurs, while the upper punches are usually located within the dies. If the compact is noncircular, for example quadratic, a rotation of the punches or the inserts, respectively, is not suitable.
The invention is based on the problem to create a rotary press in which an adherence of the compact or of material of the compact is not possible also for a noncircular cross-sectional shape of the dies.